I have a 1974 Ford F250 4x4 with a snow plow on it, put the plow on last year, has a 360 with the C6 trans, question is sometimes it goes in gear right away others i have to rev it way up then it goes, and after act like nothing ever was wrong, going down the highway it works and shift as it should, if i run it for along time it works without problems, unless i let it idle for a long period of time in park then it acts up for the first time going into forward, no probs with reverse at all, just forward, if I manually shift it to low and up it still does it....replaced the fluid and filter and still does it...fluid was not burnt at all..has me stumped as to what could be wrong with it...Thanks for any and all help..Bob